1. Field of the Invention
The present invention relates to a hydrostatic continuously variable transmission that can be used in two-wheel motor vehicles or automobiles, and which includes a hydraulic pump with a cam plate having a fixed angle of inclination and a hydraulic motor with a cam plate having a variable angle of inclination which are connected to each other via a closed hydraulic circuit consisting of a low pressure oil route and a high pressure oil route.
2. Description of Background Art
In hydrostatic continuously variable transmissions equipped with a fixed displacement cam plate type of hydraulic pump and a variable displacement cam plate type of a hydraulic motor, where the pump cylinder and motor cylinder are integrated, the gear ratio is obtained by the following formula, resulting in an actual gear ratio of about 1 to 3.
Gear ratio=1+(hydraulic motor volume/hydraulic pump volume)
In order to get the vehicle moving by slipping the clutch during the transfer of power from the input members to the output members using such a hydrostatic continuously variable transmission, the high pressure oil route connected to the hydraulic pump has conventionally been outfitted with a clutch valve (operated by means of the centrifugal governor); the clutch valve opens when the vehicle gets underway, allowing the hydraulic pressure of the high pressure oil route to be released to the discharge port, and the clutch valve gradually closes with the increase in revolutions, allowing the hydraulic pressure of the high pressure oil route to reach the hydraulic motor.
In Japanese Laid-Open Patent Application 63-111362, the phase in the direction of eccentricity of the eccentric ring that actuates the distributing valves of the hydraulic pump is varied to improve the pumping efficiency of the hydraulic pump.
However, when a hydrostatic continuously variable transmission is equipped with a clutch valve to start the vehicle moving, not only is the complex structure a problem, but the operating stability is diminished by variations in the oil temperature.